Understanding tsunami alert messages

For preparedness tips, visit: • www.ready.gov • http://ptwc.weather.gov

NOAA Pacific Tsunami Warning Center

(Editor’s note: A tsunami watch for Hawaii was canceled on Jan. 22 following a magnitude 7.9 earthquake off Alaska.)

Hawaii is at risk from tsunamis caused by both distant (“teleseismic”) and local sources. The Pacific Tsunami Warning Center (PTWC) issues different message types for tsunamis generated by these two types of sources. Tsunami messages are issued to notify emergency managers and other local officials, the public and other partners about the potential for a tsunami following a possible tsunami-generating event.

Tsunami message types:

Tsunami warning: It is issued when a potential tsunami with significant widespread inundation is imminent or expected. Warnings alert the public that widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after arrival of the initial wave.

Tsunami watch: It is issued to alert emergency management officials and the public of an event which may later impact the watch area. The watch area may be upgraded to a warning or advisory — or canceled — based on updated information and analysis.

Tsunami advisory: It is issued due to the threat of a potential tsunami which may produce strong currents or waves dangerous to those in or near the water. Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory.

Tsunami information statement: It is issued to inform emergency management officials and the public that an earthquake has occurred. In most cases, information statements are issued to indicate there is no threat of a destructive tsunami and to prevent unnecessary evacuations as the earthquake may have been felt in coastal areas.

Tsunami seismic information statement: It is issued to inform emergency management officials and the public that an earthquake has occurred, and determines the likelihood of tsunami impact and preliminary details of the earthquake magnitude. These messages are issued to prevent unnecessary evacuations.

Tsunami warning cancellation: A final product indicating the end of the damaging tsunami threat. A cancellation is usually issued after an evaluation of sea level data confirms that a destructive tsunami will not impact the warned area.

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